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So you want PWM control of your 3-pin fan?

madmalkav

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I bought a Gelic Icy Vision for my wife GPU just to discover that even if it comes with a VGA PWM connector it doesn't have the PWM pin, nor do the fans support PWM. Both fans are cable to a single VGA PWM connector.

I will love to make a version of this circuit for controlling these fans with the graphic card VGA signal. I only need to control this two fans so I think I can save a lot of space in connectors etc. But I know nothing about electronics, I'm the kind of guy that solder stuff without understanding how it really works, so any help will be appreciated.
 

tedlas

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I had to start a new thread because I couldn't update the old one.

Here's the improved mosfet version of the 4pin pwm to 3pin fan circuit. This is closer to Intel's spec which allows for up to 5.25v pull-up and 5ma on the pwm pin. This is 5.15v and 1.2ma. Any logic-level n-channel mosfet capable of a few amps will work fine.

Tested, working. Enjoy.

I am very very happy I found this thread! I have been playing around inside of a simulator type thing, but it doesn't seem right.

Can someone explain what is going on? Is everything happening the way it should?
 

dmax

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It is my belief that the information w.r.t. this design is incorrect, for these reasons:
That by locating the PWM Mosfet in the Earth line, it can 'Modulate' the Hall Effect device, and that
by so doing, produces a PWM signal on the Tacho. feed lead.
I think that the (Intel) spec. requires the PWM control to be in the Pos. line, and therefore, the supply
voltage is relatively uninfected; That it can run from 5 or 12 volt line.
Here is a link, for anyone needing further info:-
http://www.maximintegrated.com/en/app-notes/index.mvp/id/3530
http://para.maximintegrated.com/en/results.mvp?fam=fan_cntrl
 
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It is my belief that the information w.r.t. this design is incorrect, for these reasons:
That by locating the PWM Mosfet in the Earth line, it can 'Modulate' the Hall Effect device, and that
by so doing, produces a PWM signal on the Tacho. feed lead.
I think that the (Intel) spec. requires the PWM control to be in the Pos. line, and therefore, the supply
voltage is relatively uninfected; That it can run from 5 or 12 volt line.
Here is a link, for anyone needing further info:-
http://www.maximintegrated.com/en/app-notes/index.mvp/id/3530
http://para.maximintegrated.com/en/results.mvp?fam=fan_cntrl
All of that had been mentioned in the thread.
 

dmax

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The reason that I came to this link, is because I was looking for a quick design to run a (5 volt) Blower (think laptop)
in an HTPC, and most available fans are of a 3 wire configuration.
I have now re-read this thread, and appreciate that some of the points had been covered.
In your response (57), you said that Intel had made it 'complicated', but they didn't, it was the only Logical way that the
system could be developed; By that, I mean that one would Naturally have the Tacho. output, referenced to Ground,
and therefore, the Hall Effect Device, will be Low-sided, which is where the Rotor coils are switched.
Therefore, the only place to PWM the motor, is on the High-side.
Maybe, I don't see that it was ever an option to Low-side the PWM control on a 3 wire motor.
As an update, it would be appreciated if you could present a circuit, which incorporates a High-sided Mosfet element,
as these are better suited to this process, than any bi-polar transistor.
Regards.
 
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High side switching via. MOSFET will require gate drive >12v. Use a BJT transistor. Because it's switched mode, losses are minimal. Typically (.6V*A)*PWM=dissipation. If you had 3 amps worth of fans (a lot), and PWM is 100%, you will only have ~1.8w of heat to dissipate from the transistor.

I'm totally swamped in projects right now. I don't think I can get to a schematic any time soon but BJTs are fairly easy to drive. A small TO92 device to drive a TO220 device is fairly simple.
 
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It's going to be something along these lines. Not sure how it will work with the PWM signal being 5v but a low/hi signal driving this circuit will give you a low/hi out. Choose a Q1 large enough to drive your load, Choose R2 to drive enough current into Q1's base. Q2 should be large enough to shunt Q1's base current. R1 can be 10k or higher or even left out.
 

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It's going to be something along these lines. Not sure how it will work with the PWM signal being 5v but a low/hi signal driving this circuit will give you a low/hi out. Choose a Q1 large enough to drive your load, Choose R2 to drive enough current into Q1's base. Q2 should be large enough to shunt Q1's base current. R1 can be 10k or higher or even left out.
Hi Lazzer

So I want to use this circuit for my ASUS M5A97Evo, and my water cooling CM nepton 120XL pump that has 3 wires.
I noticed my cooler pump is not running at full speed while conected to the motherboard. So can i use your first circuit with a 12V molex connector?
Somthing like image attached.

Sorry for my bad english
 

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Hi Lazzer

So I want to use this circuit for my ASUS M5A97Evo, and my water colling CM nepton 120XL pump that has 3 wire.
I noticed my cooler pump is not running at full speed while conected to motherboard. So can i use your first circuit with a 12V molex connector?
Somthing like image attached.

Sorry for my bad english
I can't answer your question, but your english is fine just so you know. :)
 

dmax

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I can't answer your question, but your english is fine just so you know. :)
Just a quick reply; You do not need anything as complicated as the above circuit, as your Pump has only 3 wires, there is NO PWM
control signal, so, just use the 3 connector plug, into you Mother-board, where the 3rd wire will indicate the Pump motor Speed.
A google search linked me to this article:-
http://www.tomshardware.co.uk/answers/id-2051351/fan-fan-header-problem-asus-m5a97.html
So it may be worth checking the settings in your BIOS.
Regards,
 
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Just a quick reply; You do not need anything as complicated as the above circuit, as your Pump has only 3 wires, there is NO PWM
control signal, so, just use the 3 connector plug, into you Mother-board, where the 3rd wire will indicate the Pump motor Speed.
A google search linked me to this article:-
http://www.tomshardware.co.uk/answers/id-2051351/fan-fan-header-problem-asus-m5a97.html
So it may be worth checking the settings in your BIOS.
Regards,
No actually my bigger problem is that my motherboard doesn't support fan voltage control through CPU connector and it's running at full speed all the time, and here is my second problem, my pump can't reach its max speed through motherboard CPU connector.
 
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dmax

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No actually my bigger problem is that my motherboard dose not support fan voltage control through CPU connector and its running at full speed all the time, and there's my second problem, my pump can't reach its max speed through motherboard CPU connector.
Let's be Very specific; Fan Speed control is not regulated by Voltage, but by PWM, and, by convention, any 3 pin fan connector WILL power the fan at Full voltage,
and hence, Full Speed; The only variation, is via. the 4th wire, which regulates the Fan Speed by virtue of the control circuit of the Fans internal Ground connection.
(There is an indication that some units seem to be 'better' powered from the Molex (chassis) plug, but I'm not convinced that, That is the problem).
Your original complaint, was that the Pump was not running at Full Speed; Do you know this as a fact, i.e. via. an On-screen, Tacho readout?
The circuit you submitted, will not work, for various reasons, that is why any Added control, Has to be in the 12 volt line (all due to backward compatibility).
If your Cooler pump is not running at full speed, does it do so when connected directly to the 12 volt connector, and can you explain the difference.
Regards,
 

andrew124c41

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I had to start a new thread because I couldn't update the old one.

Here's the improved mosfet version of the 4pin pwm to 3pin fan circuit. This is closer to Intel's spec which allows for up to 5.25v pull-up and 5ma on the pwm pin. This is 5.15v and 1.2ma. Any logic-level n-channel mosfet capable of a few amps will work fine.

Tested, working. Enjoy.

I have a bunch of M5A97 MBs LE and non LE R2.0 with AMD processors. I am new at doing PC builds and I bought a bunch of coolermaster led 120s that run a 2000 rpm. I want to run 4 fans intake and 3 fans exhaust. These are 3 pin fans. I have heard but am not certain, that the PWM MB control in bios or fanExpert will only slow them down to 60%. I thought that perhaps using two of these circuits running the fans in parallel to the two separate case fan headers would work. It is not clear to me why one can draw power directly from the PSU yet have control...guess it is the MOSFET.

I saw a circuit with simply an NPN power transitor and a 100 k potentiometer but I don't think the voltage would drop below 5 volts.
 

dmax

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I still maintain that this circuit will not function correctly, with standard Computer Fans, for the reasons in my previous reply.
By Pulsing the Ground Lead, you interfere with the Switching Transistors which energise the Motor Coils; That is why the control HAS to be in the 12 volt supply line,
all due to backward compatibility.
 

andrew124c41

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I still maintain that this circuit will not function correctly, with standard Computer Fans, for the reasons in my previous reply.
By Pulsing the Ground Lead, you interfere with the Switching Transistors which energise the Motor Coils; That is why the control HAS to be in the 12 volt supply line,
all due to backward compatibility.
I have been able to control 3 pin fans by decreasing the voltage with resistance. I assume you are talking about 4 pin fans. It was my understanding that the fans are the same in terms of their being simple DC motors, just that the PWM fans' speed is controlled by duty cycle. They have a PWM circuit built right into the fan. I thought this circuit merely duplicated what is in the fan. I am referring to the circuit that Blackboy posted? Will that work for me. Also, I had heard that PWM would only bring the speed down to 60%. I may just have to get rid of these fans unless anyone has a solution. I have attached a two component circuit and wonder if it will work. for what I am trying to do...I would have two of these
 

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I have a bunch of M5A97 MBs LE and non LE R2.0 with AMD processors. I am new at doing PC builds and I bought a bunch of coolermaster led 120s that run a 2000 rpm. I want to run 4 fans intake and 3 fans exhaust. These are 3 pin fans. I have heard but am not certain, that the PWM MB control in bios or fanExpert will only slow them down to 60%. I thought that perhaps using two of these circuits running the fans in parallel to the two separate case fan headers would work. It is not clear to me why one can draw power directly from the PSU yet have control...guess it is the MOSFET.

I saw a circuit with simply an NPN power transitor and a 100 k potentiometer but I don't think the voltage would drop below 5 volts.
This is true you can slow them down to 60 but they only run between 60 and 100 duty cycle.
The screwed up thing about these ASUS boards is they have a min/max temp setting in BIOS but only 3 pin fan headers on the board. lol and you can't set the temp below 40c.

But I have 7/8 casefans running on a HAF X and they do a fine job, not too noisy and not too quiet. :p




Oh instead of AI SUITE you can use Argus Monitor to control fan speed if you wish, or AMDOD but that doesn't work as good.
 

dmax

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I have been able to control 3 pin fans by decreasing the voltage with resistance. I assume you are talking about 4 pin fans. It was my understanding that the fans are the same in terms of their being simple DC motors, just that the PWM fans' speed is controlled by duty cycle. They have a PWM circuit built right into the fan. I thought this circuit merely duplicated what is in the fan. I am referring to the circuit that Blackboy posted? Will that work for me. Also, I had heard that PWM would only bring the speed down to 60%. I may just have to get rid of these fans unless anyone has a solution. I have attached a two component circuit and wonder if it will work. for what I am trying to do...I would have two of these
I have been able to control 3 pin fans by decreasing the voltage with resistance. I assume you are talking about 4 pin fans. It was my understanding that the fans are the same in terms of their being simple DC motors, just that the PWM fans' speed is controlled by duty cycle. They have a PWM circuit built right into the fan. I thought this circuit merely duplicated what is in the fan. I am referring to the circuit that Blackboy posted? Will that work for me. Also, I had heard that PWM would only bring the speed down to 60%. I may just have to get rid of these fans unless anyone has a solution. I have attached a two component circuit and wonder if it will work. for what I am trying to do...I would have two of these
 

dmax

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The fact that The/A, motor runs on DC, only describes part of its Specification.
ALL (as far as I am aware) use Switched Transistor's in the ground lead, which is controlled
by a Hall Effect sensor (Switch), and a 3 wire fan works on 12 volt, (or 5 volt in laptops).
It IS possible to reduce the operating voltage, but this is a notoriously problematic solution, that is
why PWM (4 wire) fans run at 12 volts, with a varying PWM signal, (THEY DO NOT REDUCE THE VOLTAGE).
If I remember correctly, the Intel spec. requires the Electronic control, to push a continuous12volts for 1-2 seconds, in order to overcome the Start-up resistance (sort-of, like Stiction).
In order for you to use 3 wire motors (IF your Motherboard does not have PWM Case Fan Header), is
to find a circuit, which converts the Output of a Thermocouple, to PWM, and feed THAT to the (12 volt)
supply line,; Though it would probably be easier to use a Fan which has a Remote Thermal Sensor.
 

andrew124c41

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This is true you can slow them down to 60 but they only run between 60 and 100 duty cycle.
The screwed up thing about these ASUS boards is they have a min/max temp setting in BIOS but only 3 pin fan headers on the board. lol and you can't set the temp below 40c.

But I have 7/8 casefans running on a HAF X and they do a fine job, not too noisy and not too quiet. :p




Oh instead of AI SUITE you can use Argus Monitor to control fan speed if you wish, or AMDOD but that doesn't work as good.

With 60 percent duty cycle, do you know how much they will slow down from 2,000 rpm?
The fact that The/A, motor runs on DC, only describes part of its Specification.
ALL (as far as I am aware) use Switched Transistor's in the ground lead, which is controlled
by a Hall Effect sensor (Switch), and a 3 wire fan works on 12 volt, (or 5 volt in laptops).
It IS possible to reduce the operating voltage, but this is a notoriously problematic solution, that is
why PWM (4 wire) fans run at 12 volts, with a varying PWM signal, (THEY DO NOT REDUCE THE VOLTAGE).
If I remember correctly, the Intel spec. requires the Electronic control, to push a continuous12volts for 1-2 seconds, in order to overcome the Start-up resistance (sort-of, like Stiction).
In order for you to use 3 wire motors (IF your Motherboard does not have PWM Case Fan Header), is
to find a circuit, which converts the Output of a Thermocouple, to PWM, and feed THAT to the (12 volt)
supply line,; Though it would probably be easier to use a Fan which has a Remote Thermal Sensor.
The motherboards I have use 4 pin PWM control. As I understand, 2 lead fans simply run on 12 v. What you are refering to is the inertia, the startup volaage could be around 5 v plus or minus a volt or two, fan dependant. 3 pin fans as you said use the third lead to utilize the Hall effect to determine speeed. The forth lead gives the information so to speak, to use pulse width to manefest as a duty cycle.

I am just trying to figure out how, having purchased these 2,000 rpm fans, I might be able to bring them down to around 800 rpm. Sure, I could do it permently with a large resister for each set of fans...but simple control would be nice. I was just trying to find out if the circuit that started this thread by Lazer408 can work for my situation. I also poste a pic of a simple two compnant schematic with a power npn and a 100 ohm pot that should be able to do this manually...I wonder if that will work.
 

dmax

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NO, you cannot rely upon them Starting on 5-7 volts, for the reason that I alluded to in my previous reply.
In order for them to start reliably, they must start at 12 volts, then be reduced.
The stupid aspect w.r.t. using a power resistor, is that it WILL generate vast amounts of Heat, (relatively).
If you were to use anything, then reference the following:-
http://www.ebay.co.uk/itm/DC-12V-40V-5A-PWM-DC-Motor-Variable-Speed-Controller-Reversible-Switch-Regulator-/261978141832?pt=LH_DefaultDomain_3&hash=item3cff1d3488
 
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Sorry, seems I told a lie. I just double checked and at least 3 of the headers are actually 4 pin.

It's the fans which are 3 pin. :oops:

This applies to Sabertooth and M5A97, I have both.


And I should mention I have a 12v .40A Fractal Design 140mm which needs a push start every now and again if I use 60% duty.


But the 200mm Coolermasters which are 12v .30A fire up every time
 
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dmax

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It's usually smart to attach some sort of heatsink to the mosfet "backside". Half of the chipset cooler should do the trick. Or an aluminium VRAM heatsink (cube shaped). Stuff that you can easily obtain from anywhere.
 

andrew124c41

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Sorry, seems I told a lie. I just double checked and at least 3 of the headers are actually 4 pin.

It's the fans which are 3 pin. :oops:

This applies to Sabertooth and M5A97, I have both.


And I should mention I have a .40A Fractal Design 140mm which needs a push start every now and again if I use 60% duty.


But the 200mm Coolermasters which are .30A fire up every time
Forgive me, I am not sure I understand.
You have the same MB and 3 pin fans as I do.
How are you controlling the 3 pin fans?
Is it just with the software or are you using a circuit?
Finally, at 2,000 RPM, how fast do you think my 120s will go?
Further to my above recommendation, I would suggest the following:-
http://www.ebay.co.uk/itm/PWM-DC-12V-2A-Adjustable-Motor-Speed-Controller-for-Brushless-Fan-/261978142374?
Or:-
http://www.ebay.co.uk/itm/DC-Motor-Speed-Regulator-Controller-Switch-6V-12V-24V-3A-PWM-/252035720628?
as it runs at 21KHz, which is better than the 15kHz of the previous one.
Ideally, you would be looking for 25kHz, as any 'cogging' will be above the upper range of Audibility.
@dmax
Forgive me, maybe you did not understand what I was saying....I agree with you. I was refering to the reason that they cannot be started at 5 v....the inherent inertia. Once going, they can be reduced.

I had seen the PWM controlers that you refert to on Amazon in the US. However, I was not sure if they would work. The power transitor I picked is capable of dissipating the heat.

What I have been trying to find out are two things:

1) Will the circuit with the MOSFET work with my MB. That is, will the fan speed be controlled and can it be manually controlled via the UEIF or FanExpert? Can I get the speed below 1,000 rpm this way?
2) If #1 will not work, then I either want to use the power transister or one of the pwm controllers you suggested...one for each set of fans intake and exhaust.
 
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Forgive me, I am not sure I understand.
You have the same MB and 3 pin fans as I do.
How are you controlling the 3 pin fans?
Is it just with the software or are you using a circuit?
Finally, at 2,000 RPM, how fast do you think my 120s will go?
OK, the chassis fan headers can control 4pin pwm fans but in DC, not pwm.. The CPU fan header is the only true PWM.

I control case fan speed by adjusting min/max duty cycle, (not really duty cycle but that's what bios says lol) speed stays constant but at min 60 I hardly hear my fans.

In saying that, I had a 120mm Coolermaster which got a bit noisy.... so I removed it. Not sure on your specific fans.






Also, did you ask about a water pump, I can't remember.....but if you did, what u can do is get one of these: https://shop.ekwb.com/ek-dcp-4-0-pwm-12v-dc-pwm-pump

It uses a molex plug for power, but comes with a 4pin pwm connector. Plug the connector into the CPU fan header and you have temp controlled fan speed.
 
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